A keyboard device is widely used as an input device of an electronic device such as a personal computer. For example, Japanese Laid-open Patent Publication No. 2000-173389 discloses a technique in which a pair of members having a gear mechanism are provided on a sheet. Japanese Laid-open Patent Publication No. 2001-155580 discloses a technique in which a key top moves up and down by rotationally moving a decussate member. Recently, a portable electronic device such as a note-type personal computer (i.e., a notebook PC) is widely used. For convenience of portability, weight saving and downsizing are required of the electronic device. In view of this, thinness is required of the keyboard device.